Largely Nocturnal Kangaroo Rats Preyed Upon by Diurnal American Kestrels in New Mexico

Abstract

As secondary cavity nesters, American Kestrels (Falco sparverius) adapt readily to nest boxes, so most documentations and enumerations of their prey have been from boxes during the approximately 30-d nestling period (Smallwood and Bird 2020). Sherrod (1978), summarizing six North American studies of American Kestrel prey by numbers, not mass, showed that invertebrates (74%) were most often captured, though mammals (16%), birds (9%), and reptiles (1%) were also taken. However, in 2017 at 975 m elevation in the semi-arid southern Great Plains of northwestern Texas, reptiles (74.8%) were by far the most frequent kestrel prey recorded on motion-activated video cameras, while invertebrates, mammals, and birds made up 18.2%, 4.4%, and 2.9%, respectively (Boal et al. 2021). Of 187 mammals documented, 121 (64.7%) recorded were .42 g and ,75 g (Boal et al. 2021), which represented 38– 68% of the mass of an average 110-g American Kestrel male (Smallwood and Bird 2020). Thus, the capability of this species to repeatedly capture prey up to two-thirds their own mass has been previously reported. From 1995 to 2020 American Kestrels occupied one (n1⁄4 14) or both (n1⁄4 11) of two nest boxes 250 m apart in the Eldorado at Santa Fe (ESF) subdivision 15 km south of Santa Fe, New Mexico, USA. They successfully fledged young on 35 of 36 (97.2% fledging success) attempts during 50 (72% occupancy rate) nest box years; the second box became available in 1997. ESF is at 2000–2100 m elevation in piñon pine (Pinus edulis)-juniper (Juniperus spp.) savannah with groundcover dominated by blue grama (Bouteloua gracilis); it was converted from ranchland to housing starting in 1972. Large lots (0.5–1 ha), limits to yard/garden size, and extensive greenbelts resulted in a largely intact, ungrazed, natural habitat and prey base. Prey deliveries to one box regularly observed were approximately 67% (n1⁄4 29) reptilian between 1996 and 2009, though observations were opportunistic rather than standardized (Stahlecker and Cartron 2010). I visited nest boxes to band nestlings 2–3 wk after I began to see prey deliveries. I usually ignored the conglomeration of prey remains, particularly legs and carapaces of invertebrates, to complete the banding in a minimal time. However, on 8 July 2018, I found five tails of Ord’s kangaroo rats (Dipodomys ordii) in Box 1, and an additional tail in Box 2. The typical mass of D. ordii is approximately 52 g (Jones 1985), or 47% of the mass of an average American Kestrel male. The young in Box 1 were 13–15 d old and those in Box 2 were 7–10 d old, based on a photographic guide (Griggs and Steenhof 1993). The D. ordii were likely brought to the boxes by the males, as females forage very little early in the nestling period, but instead brood, feed, and defend the nestlings (Smallwood and Bird 2020). No species of kangaroo rat has, to my knowledge, been previously reported as prey of the American Kestrel. All 20 species in the genus Dipodomys are primarily nocturnal granivores (Lockard and Owings 1974, Reichman and Price 1993) that would seem to be unavailable to diurnally active raptors. The Dipodomys possibly were scavenged from Great Horned Owls (Bubo virginianus) nesting nearby (Stahlecker 2015), but I have watched both adult and 3-wk-old nestling owls swallow Dipodomys hindquarters including the entire tail, so they likely leave nothing to scavenge. Further, there have been only two published cases of scavenging by American Kestrels, both in winter; items eaten were a decomposed Eastern Screech-Owl (Megascops asio; Ganis 1976) and a large domestic turkey (Meleagris gallopavo; Schulwitz et al. 2019). Kangaroo rats have been reported as prey items for four species of diurnal raptors, including Swainson’s Hawk (Buteo swainsonii; Bednarz 1988; Dipodomys spp.; Snyder and Snyder 1991; D. spectabilis), Harris’s Hawk (Parabuteo unicinctus; Bednarz 1988; Dipodomys spp.), Ferruginous Hawk (B. regalis; Olendorff 1993; 92.5% D. ordii; Cartron et al. 2004; D. ordii), and Prairie Falcon (Falco mexicanus; Steenhof 2020; Dipodomys spp.). Similarly, Daley et al. (2000) reported predation by the diurnal Loggerhead 1 Email address: dale@eagleenvironmental.net